Building Design for Moderate Seismic Regions

The authors' firm practices in the northeast, where steel frames are routinely more cost-effective than cast-in-place concrete frames, and ordinary concentric braced frames are the preferred lateral force resisting system where architectural constraints allow. This paper discusses how Building Code and Reference Standard revisions have affected the design, detailing, fabrication and erection of these preferred structural solutions, and how research into the influencing factors behind Code revisions enhances cost-effective solutions. The design case studies are all taken from the Commonwealth of Massachusetts which, for the time period of 1997 to 2008, permitted construction projects under the 6^th Edition of the Massachusetts State Building Code, which is based on BOCA 1997 (ASCE 7-95) and certain prescriptive exceptions which result in most buildings being designed for Seismic Design Category C, including special seismic detailing consistent with the 1992 AISC Seismic Provisions. Spectral design acceleration values for Massachusetts under the 6^th Edition are based on: Sa = .12g; T = H_n^.75/50; Site Factors = 1, 1.2, 1.5, and 2. Wind forces in the Mass Code 6^th Edition are based on fastest-mile wind speeds of 90 mph with standard exposure coefficients and no breakdown of leeward and windward forces.